System for preventing contaminant dispersal in insulating fluid of electrical apparatus

ABSTRACT

A system for use in electrical apparatus having contacts immersed in a body of insulating fluid and adapted to open and close causing arcing therebetween which produces contaminants in the fluid. The system includes a compartment for relatively closely confining said contacts, a fluid inlet in said compartment, a filter, and means, including a pump, for withdrawing fluid from the compartment through the inlet, pumping the withdrawn fluid through the filter, and returning the filtered fluid to said body of fluid. Contaminants produced in the fluid in the compartment by arcing of the contacts are thus filtered without being permitted to disperse throughout the body of fluid. As a method of preventing contaminant dispersal, the disclosure teaches withdrawing fluid of the body from a location closely adjacent the contacts, filtering the withdrawn fluid to remove the contaminants and subsequently returning the filtered fluid to the body of fluid.

United States Patent 91 Hucker et al.

[54] SYSTEM FOR PREVENTING CONTAMINANT DISPERSAL IN INSULATING FLUID OF ELECTRICAL APPARATUS [75] Inventors: Arthur A. Hucker, Normandy; David F. Winter, Kirkwood, both of Mo.

[73] Assignee: Central Transformer, Inc., Pine I Bluff, Ark.

[22] Filed: Jan. 20, 1971 21 Appl. No.: 108,095

FOREIGN PATENTS OR APPLICATIONS 2/1964 Canadamr. 200/14 5 51 May 1, 1973 964,827 7/1964 Great Britain ..200/l48 E Primary Examiner-Robert S. Macon Attorney-Keenig, Senniger, Powers and Leavitt [5 7] ABSTRACT A system for use in electrical apparatus having contacts immersed in a body of insulating fluid and adapted to open and close causing arcing therebetween which produces contaminants in the fluid. The system includes a compartment for relative- 1y closely confining said contacts, a fluid inlet in said compartment, a filter, and means, including a pump, for withdrawing fluid from the compartment through the inlet, pumping the withdrawn fluid through the filter, and returning the filtered fluid to said body of fluid. Contaminants produced in the fluid in the compartment by arcing of the contacts are thus filtered without being permitted to disperse throughout the body of fluid. As a method of preventing contaminant dispersal, the disclosure teaches withdrawing fluid of the body from a location closely adjacent the contacts, filtering the withdrawn fluid to remove the contaminants and subsequently returning the filtered fluid to the body of fluid.

14 Claims, 7 Drawing Figures OIL FROM OTHER PHASES 4 Paitented May 1, 1973 3 Sheets-Sheet 2 Frill/4 a:

FIG. 5

Patented May 1, 1973 3 Sheets-Sheet 5 SYSTEM FOR PREVENTING CONTAMINANT DISPERSAL IN INSULATING FLUID OF ELECTRICAL APPARATUS BACKGROUND OF THE INVENTION The invention relates to apparatus and methods for removing contaminants from insulating fluid, and more particularly to such apparatus and methods for use in electrical apparatus having arc-producing contacts immersed in a body of insulating oil.

In electrical power apparatus, such as transformer load tap changers, wherein contacts (such as for effecting load transfer) are immersed in a body of insulating fluid such as oil, arcing between the contacts resulting from closing and opening operations thereof tends to produce contaminants, e.-g., particles or clouds of carbon, in the oil. These contaminants tend to disperse throughout the body of oil and may eventually cause contamination of such an extent that the insulating properties of the oil are degraded sufficiently that breakdown of the oil may result, causing contact failure or short-circuiting, etc., and necessitating costly equipment shut-down and repairs. Load tap changer failure in a substation transformer, for example, may produce a power outage which interrupts customer service over a widespread area.

It has been proposed to filter the entire volume or body of oil in which the arc-producing contacts are immersed, either continuously or at intervals. This has not been found to be efficient, however, since the contaminants, such as carbon and other particles, are not removed as they are formed and are therefore given an opportunity to disperse throughout the entire volume of oil. Accordingly, not only must a possibly rather considerable total volume of oil be refiltered time and time again, but filtration of the entire volume of oil is excessively time-consuming. Moreover, filtration of the entire volume of oil does not ensure that any localized concentration of contaminants closely adjacent the contacts will be eliminated, noting that such contaminants may require a relatively long period of time to disperse throughout the entire volu'me. Such a local concentration may build up to excessive levels.

' BRIEF SUMMARY OF THE INVENTION Among the several objects of the invention may be such a system and methods for removing carbon and other particulate contaminants as they are formed during contact operation; the provision of such a system and methods which are highly-efficient and which ensure the elimination of localized concentration of contaminants; and the provision of such a system which is very simply and economically manufactured. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, the invention involves, in one aspect, a system for use in electrical apparatus such as a transformer load tap changer, having contacts immersed in a body of insulating oil and adapted for opening and closing operation causing arcing therebetween which produces contaminants in the oil. The system includes a compartment within the body of oil and of a relatively small volume which relatively closely confines said contacts to inhibit contaminant dispersal. The com partment has an aperture for permitting flow of oil from the body of oil into the compartment but tending to confine in the compartment contaminants produced by contact arcing. The compartment is provided with an oil inlet. A pumping arrangement withdraws oil from the compartment through the oil inlet, pumps the withdrawn oil through a filter, and then returns the filtered oil to the body of oil. Preferably, circuit means is provided for causing pumping operation for a time period beginning substantially concurrently with operation of the contacts. In this way, contaminants produced in the oil in the compartment by contact arcing are filtered out and thereby removed without being permitted to disperse throughout the body of oil.

The invention involves in another aspect the method of preventing contaminants-from dispersing throughout the oil which comprises withdrawing oil from a location closely adjacent the contacts, filtering the withdrawn oil so as to remove contaminants therefrom, and then returning the filtered oil to the body of oil.

BRIEF DESCRIPTION THE DRAWINGS FIG. I is a pictorial representation, tive, of a system of the invention;

FIG. 2 is a perspective view of one embodiment of a compartment of the invention;

FIG. 3 is a vertical section of the compartment of FIG. 2;

partly perspec- FIG. 4 is a perspective view of another compartment embodiment;

FIG. 5 .is a vertical section of the compartment of FIG. 4;

FIG. 6 is a fragmentary perspective view of yet another compartment embodiment; and

FIG. 7 is a schematic circuit diagram of control circuitry of the invention. I

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and more particularly to FIG. 1, illustrated generally at I1 is a switching assembly including a shaft 13 which can be turned to move a movable contact 15 so that it closes and opens from a stationary contact l7. Assembly 11 is illustrated Shaft 13 extends through an insulating barrier panel 19 which may be one of three such panels dividing the tap changer into three circuit phases. There is a switching assembly on each face of panel 19 and these assemblies may be symmetrical with respect to the panel or identical, et cetera.

In accordance with this invention, a rectangular enclosure or compartment, designated generally 21, is secured as by means of screws 23 through flanges 25 of the compartment, to panel 19. Compartment 21 encloses switching assembly 11 and thus relatively closely confines contacts and 17 of assembly 11. A similar compartment 21' is provided for the opposite side of panel 19, and there are similar compartments for the other panels of the tap changer apparatus enclosing other sets of contacts for other phases. As will be apparent, the volume of any one ofthese compartments is substantially less than the volume of oil in the tank itself.

Compartment 21 is open at the top and the top edge 27 thereof is positioned above the oil level 29, as illuspartment bottom). Notwithstanding its open bottom,

compartment 21 tends to confine contaminants produced by arcing of contacts 15 and 17. Compartment 21 (and, of course, each of the other compartments) is provided with a suitable aperture 31 in the front wall 33 thereof through which extends shaft 13. In order to facilitate installation of compartment 21 without requiring removal of shaft 13 and disassembly of contacts, etc., the compartment may be in the form of overlapping halves. Thus, there may be two halves designated generally 35a and 35b which are overlapped at 37 as illustrated. Accordingly aperture 31 is defined by a U-shaped slot in the edge of each of halves 35a'and 35b. The material used for compartment 21 is preferably electrically insulating, such as paper fiber.

An oil collection tube 39 extends through another aperture 31 in wall 33 and this aperture, too, may be defined by U-shaped slots in the edges of halves 35a and 35b. Tube 39 is positioned so that it extends across and above the top edge (or may rest on the edge), designated 43, of panel 19 but below the oil level 29 in the tank. This arrangement obviates drilling of the panel to accommodate tube 39. Tube 39 is provided with one or more oil inlet apertures 44 within compartment 21. Of course, similar apertures are provided in each of the other compartments.

An oil pumping and filtering arrangement is provided for withdrawing oil from compartment 21 through apertures 44 and includes a suitable electrically operated pump 45, such as a gear pump, located outside the tank and which is connected by an oil line 47 to can deliver about 5 gallons per minute, for example. This pumping and filtering arrangement withdraws and filters out contaminants produced in the oil in each of the compartments by arcing of the contacts, e.g., 15 and 17. This allows the contaminants to. be removed without being permitted to disperse throughout the body of oil in the tank.

Referring to FIGS. 2 and 3, another type of compartment of the invention is designated generally 55, and encloses and relatively closely confines arc-producing contacts of the type shown in FIG. 1. The contacts are generally centered in the compartment. Compartment is rectangular and includes an outer portion including a front wall 57 having an aperture 59 through which the contact operating shaft 13 (not shown) may extend. Wall 57 includes another aperture 61 above aperture 59 through which oil collection tube 39 is shown to extend. Compartment 55 includes side wall 63 spacing front wall 57 from panel 19. Flanges 65 extending from side wall 63 are secured as by screws 67 to panel 19, which of course serves as the rear wall of the compartment. Compartment 55 is therefore substantially identical in exterior appearance with compartment 21 of FIG. 1, but instead has a floor or closed bottom wall 69 which is particularly advantageous in the event pump 45 should fail or filter 49 should become clogged so that contaminants would tend eventually to disperse through the bottomless compartment into the main body of oil. Positioning of compartment 55 is such that the top edge 71 of the outer portion is located above the tank oil level 29 and aperture 61 is positioned at a level permitting collection tube 39 to extend across and above the top edge 43 of panel 19 (as shown in FIG. 3), and so may extend through a plurality of such compartments.

Compartment 55 includes a septum or inner panel 73 positioned parallel to barrier panel 19 but spaced closely adjacent thereto so as to provide a space 75 between panels 73 and 19 through which oil may flow. Panel 73 includes a pair of flanges 77 interposed between panel 19 and flanges 65 of the outer portion, thereby securing panel 73. Short offset portions 79 of panel 73 provide the spacing of the latter from panel 19. Panel 79 includes an aperture 81 for accommodating operating shaft 13, as well as an aperture 83 for tube 3 9. The lower edge of panel 73 is designated 85 and terminates a short .distance above the floor 69. It may be seen that space 75 provides compartment 55 with an aperture for permitting flow of oil from the oil body proper into the compartment, but tending to confine in the compartment any contaminants produced by arcing therein. Panel 73 acts as a baffle for directing the oil flow so that oil will flow, as depicted by arrows, into space 75 and down into the bottom of. the compartment and toward floor 69, thence upward past the contacts (not shown) and into oil collection inlets 44 of tube 39. The flow down toward and across floor 69 creates swirls or eddies in the oil, as arrows represent, which sweep floor 69 clean of contaminants. Compartment 55 may be of paper fiber, or other suitable materials, again preferably electrically insulating. Further, the construction may be of the split-halves type of compartment 21 shown in FIG. 1.

FIGS. 4 and 5 depict another form of a compartment of the invention and designated generally 87. Compartment 87, which is essentially similar in principle to compartment 55 of FIG. 2, comprises an inner section, designated generally 89, and an outer section, designated generally 91, relatively closely surrounding the inner section. Inner section 89 is preferably of the same general dimension and rectangular form of compartment 21 and, like the latter, is bottomless. The upper edge of inner section 89 is designated 93 and is positioned above the tank oil level 29. Apertures 95 and 97 are provided for accommodating operating shaft 13 of the contact assembly, a small portion of which is shown at 99. Flanges 101 of section 89 are suitably secured to panel 19, as with screws 103. In this embodiment, shaft 13 is depicted as being hollow, i.e., tubular in form, providing an oil passage 104. Shaft 13 is provided with one or more small apertures 105 through which oil from the compartment may be drawn into passage 104. Shaft 13 is suitably journalled in an oil collection gland or the like connected to oil line 47 (FIG. 1). Thus contaminated oil may be withdrawn from the compartment through passage 104.

Outer section 91 is also rectangular in form and in cludes a front wall 107 and side walls 109. These three walls are each parallel to and spaced a small distance from the corresponding wall of inner section 89 so as to provide a space 111 therebetween through which oil from the body of oil in the tank may flow.

Section 91 is provided with a bottom wall or floor 113 and is therefore closed. There is an aperture 115 for control shaft 13. The upper edge of section 91 is designated 11 7 and is positioned below oil level 29. Space 111 provides compartment.87 with an aperture for permitting flow of oil into the compartment but tending to confine in the compartment contaminants produced by arcing of contacts therein. From the foregoing, it may be seen that inner section acts as a baffle, like panel 73 of FIGS. 2 and 3, for directing the flow of oil in the manner indicated by arrows over the edge 117, into space 111 and toward and across floor 113, thence around the contacts and into the oil inlets 105 of operating shaft 13. The resultant swirling and eddy currents in the oil serve to flush or sweep floor 1 13 free of contaminants.

A portion of still another compartment of different form, and designated generally 1 19, is shown in FIG. 6. Compartment 119 is substantially identical in shape and form to compartment 55 of FIG. 2 with the exception of having no inner panel or septum. Only portions of the front wall 121 and a side wall 123 are shown. A flange 125 extending from side wall 123 secures the compartment to panel 19 (not shown), the latter providing a rear wall for the compartment. Shaft 13 (also not shown) may extend through an aperture 127. Compartment 1 19 includes a floor 128.

A small circular aperture 129 is positioned in front wall 121 adjacent the lower edge thereof through which oil in the tank may flow into the compartment. While aperture 129 is of sufficiently small size so as to tend by itself to confine in the compartment contaminants produced by contact arcing, further assurance of confinement of contaminants is provided by a small,

channel-like shield 131 suitably secured to front wall 121 in register with aperture 129.'Shield 131 comprises a relatively small further compartment which has a closed bottom 132 but which is open at the top to provide an aperture 133 into which oil may flow (and thence through aperture 129). Since aperture 133 is positioned above aperture 123 and, more significantly, at a level above the floor or bottom wall of compartment 119, space is provided within the compartment for settling and accumulation of contaminants. As will be appreciated, shield 131 provides abaffle arrangement for causing oil from the tank to flow into the bottom and across the floor of the compartment for flushing out contaminants which have settled therein.

Turning now to FIG. 7, circuitry is shown which operates as means for causing operation of pump 45 (FIG. 1) for a time period beginning substantially concurrently with closing and opening operation of contacts 15 and 17, etc., of assembly 11. This circuitry is adapted also to control operation of the drive motor of a load tap changer, of the type noted previously, and includes a pair of leads L1 and L2 adapted to be connected across a source of a.c. power, e.g., v.a.c., as illustrated. The electric motor of pump 45, designated M, is connected in a series circuit with a set of normally open contacts TDl between leads L1 and L2. Contacts TDl are adapted to be closed upon energization of a conventional timer or time delay relay TDR. The latter includes a second set of normally open contacts TD2 which are series-connected with the time delay relay TDR, itself, between leads L1 and L2. The sets of contacts TDI and TD2 are each adapted to close upon energization of relay TDR and to open at the end of a predetermined time delay interval following such energization.

Energization of time delay TDR for efiecting a time delay cycle of operation may be manually initiated by operating a push-button switch PBS which is connected in parallel with contacts TD2. Initial energization of relay TDR is also adapted to be effected by closing of either of two sets of normally open contacts MSLl and MSRl, each also connected in parallel with relay contacts TD2. The sets of contacts MSLl and MSL2 are each adapted to be closed by energization of respective motor starter magnetic contactors MSCL and MSCR.

Contactors MSCL and MSCR also include respective sets of contacts (not shown) which control the drive motor (also not shown) of a load tap changer of the type described hereinabove. Energization of contactor MSCL is adapted to cause energization of the drive motor to effect a lower voltage tap connection and energization of contactor MSCR is adapted to energize the drive motor to effect a raised orhigher voltage'tap connection. For this purpose, contactor MSCL is series-connected with a set of normally open contacts 135L between leads L1 and L2 and contactor MSCR is similarly series-connected with a set of normally open contacts 135R between leads L1 and L2. Contacts 135L and 135R are controlled by certain voltage-monitoring circuitry forming no part of this invention and which is therefore not shown. In any case, contacts 135L close to effect energization of contactor MSCL and contacts 135R close to effect energization of contactor MSCR in accordance with whether the load tap changer voltage is to be lowered or raised.

Contactors MSCL and MSCR include respective further sets of normally open contacts MSL2 and MSR2. These two sets of contacts are shown connected in a series circuit connected between the respective junctions of contactors MSCL and MSCR with contacts 13SL and 135R. Connected between lead L2 and the junction of contacts 135L and 135R is a camoperated tap change cycle switch TS which is adapted to close as the tap changer drive motor initiates a tap change cycle and which is adapted to open when contact stepping operation is terminated at the end of the tap change cycle.

The circuitry of FIG. 7 operates as follows: Closing of contacts 135L or 135R effects energization of either contactor MSCL or MSCR, respectively. This energizes the tap changer drive motor in the proper direction, and cycle switch TS then closes. Also, either contacts MSLl and MSL2, or MSRl and MSRZ are closed. Hence a latching circuit for maintainingenergization of contactors MSCL or MSCR (and therefore the drive motor) is established. Closing of either of contacts MSLl or MSRI energizes time delay relay TDR whose contacts TDI and TD2 then close. Closing of contacts TD2 establishes a latching circuit for maintaining energization of relay TDR for a time delay cycle. Closing of contacts TDl energizes pump motor M.

After the tap changing cycle is completed, switch PS2 then opens to deenergize the appropriate motor starter contactor MSCL or MSCR. However, time delay relay TDR remains in operation for the appropriate time delay interval, such as several minutes.

It will be understood by those familiar with load tap changers of the type described that a load transfer switch assembly operates, a tap selector switch is then tion. The circuitry of FIG. 7 operates to energize motor mined by time delay relay TDR. Hence, all contaminants which are produced in the compartment enclosing thearc-pr oducing contacts are filtered out. The method of the'present inventionof removing oil from a location closely adjacent the arc-producing contacts assures that the contaminants are removed without being permitted to disperse into the body of oil within the tank. Moreover, a compartment of the present invention' causes oil to-flow past the contacts as it is withdrawn from the compartment, thereby positively assuring removal of contaminants from the immediate area between and around the contacts.

The invention is advantageous in otherrespects. While the compartments of all embodiments constructed according to the present disclosure tend to confine the contaminants, the-closed bottom embodi ments of FIGS. 2-6 are particularly advantageous if the pump should fail to operate or the filter should become clogged. in this event contaminants would eventually settle into the main body of oil in the open bottom embodiment. In those compartment embodiments having closed bottoms as described, such contaminants would settle onto the bottom of the compartment. Accordingly, later operation of the pump (e.g., after repairs) will cause the contaminants to be flushed off the bottom and thereby removed by the swirling action of the oil entering the compartment as previously described.

It should be noted that compartments of the invention can advantageously be used in place of so-called arc chutes which are frequently employed in load tap changers of the present type as well as in similar electric power apparatus with which the present invention may advantageously be used.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of theinvention, it is intended that all matter contained in the above description or shown in the accornpanying drawings shall be interpreted as illustrative and not in a limiting sense. i

What is claimed is: I

1. A system for use in electrical apparatus having contacts-immersed in a. body of insulating liquid and adapted to open and close causing arcing therebetween which produces contaminants in the liquid adjacent said contacts, said contaminants tending eventually to disperse throughout said body of liquid, say system comprising:

a compartment positioned within said body of liquid for relatively closely confining said contacts, said compartment having a volume substantially less than the volume of said body of liquid and tending to confine said contaminants to said compartment to inhibit dispersal of the contaminants throughout said body of liquid;

a liquid inlet in said compartment;

a filter; and

means, including a pump, for withdrawing liquid from said compartment through said inlet before contaminants have dispersed si'gnificantly'beyond the confines of the compartment, pumping the withdrawn liquid throughsaid filter, and returning the filtered liquid to said body of liquid whereby contaminants produced in the liquid in said compartment by arcing of said contacts are filtered out and thus removed without being permitted to disperse throughout said body of liquid.

2. A system as set forth in claim 1 wherein said compartment includes an aperture permitting flow of liquid from said body into said compartment.

.-3. A system as set forth in claim 2 wherein said aperture and said inlet are located for causing flow of liquid past said contacts as the liquid is withdrawn.

4. A system as set forth in claim 2 wherein said compartment includes a floor,.said aperture being spaced above said floor, whereby contaminants may settle onto said floor if said pump is inoperative.

5. A system as set forth in claim 4 wherein said com partment includes baffle means for directing flow of liquid toward said floor for sweeping contaminants therefrom upon operation of said pump.

6. A system as set forth in claim wherein said inlet is spaced above said contacts.

7. A system as set forth in claim 5 wherein said compartment includes at least one wall, said baffle means comprising a panel inside said compartment adjacent said wall, said panel having a lower edge spaced above said floor.

8. A system as set forth in claim 5 wherein said compartment comprises an inner section constituting said baffle means and having an opening in the bottom thereof, and an outer section having walls relatively closely surrounding walls of said inner section, said outer section having a floor constituting the floor of said compartment, said inner section having at least one wall the lower edge of which is spaced above said floor.

9. A system as set forth in'claim 4 wherein said compartment includes a floor, said aperture being located in a sidewall of said compartment adjacent said floor,

said compartment including baffle means for directing flow of liquid from said body of liquid through said aperture and toward said floor.

- 10. A system as set forth in claim 9 wherein said baffle means comprises-a relatively small further compartment having a floor and an open'top and positioned on the exterior of said side wall in register with said aperture.

11. A system as set forth in claim 4 wherein said contacts are adapted to open and close by movement of an operating shaft extendingv from said compartment, said shaft including a liquid passage, said shaft including also at least one further aperture in said compartment communicating with said passage and constituting said liquid inlet, whereby liquid may be withdrawn fro said compartment through said passage. 12. A system for use in electrical apparatus having 10 contacts immersed in a body of insulating liquid and adapted for opening and closing operation causing arcing therebetween which produces contaminants in the liquid adjacent said contacts, said contaminants tending eventually to disperse throughout said body of liquid, said system comprising:

a compartment positioned within said body of liquid for relatively closely confining said contacts, the compartment having a volume substantially less than the volume of said body of liquid, the compartment including an aperture for permitting'flow of fluid from said body into the compartment but tending to confine in the compartment contaminants produced by arcing of said contacts;

a liquid inlet in said compartment;

means, including a pump, for withdrawing liquid from said compartment through said inlet before contaminants have dispersed significantly beyond the confines of said compartment, pumping the withdrawn liquid through'said filter, and returning the filtered liquid to said body of liquid; and

means for causing operation of said pump for a time period beginning substantially concurrentlywith operation of said contacts, whereby contaminants produced in the liquid in said compartment by arcr einoved without being permitted to disperse throughout said body of liquid.

13. A system as set forth in claim 12 wherein said means for causing operation of said pump comprises a time delay relay.

14. A system as set forth in claim 13 further comprising at least one magnetic contactor adapted to effect operation of said contacts, and also adapted toenergize said tirne'delay-relay when operation of said contacts is effected.

of said contactsare filtered out and thus 

1. A system for use in electrical apparatus having contacts immersed in a body of insulating liquid and adapted to open and close causing arcing therebetween which produces contaminants in the liquid adjacent said contacts, said contaminants tending eventually to disperse throughout said body of liquid, say system comprising: a compartment positioned within said body of liquid for relatively closely confining said contacts, said compartment having a volume substantially less than the volume of said body of liquid and tending to confine said contaminants to said compartment to inhibit dispersal of the contaminants throughout said body of liquid; a liquid inlet in said compartment; a filter; and means, including a pump, for withdrawing liquid from said compartment through said inlet before contaminants have dispersed significantly beyond the confines of the compartment, pumping the withdrawn liquid through said filter, and returning the filtered liquid to said body of liquid whereby contaminants produced in the liquid in said compartment by arcing of said contacts are filtered out and thus removed without being permitted to disperse throughout said body of liquid.
 2. A system as set forth in claim 1 wherein said compartment includes an aperture permitting flow of liquid from said body into said compartment.
 3. A system as set forth in claim 2 wherein said aperture and said inlet are located for causing flow of liquid past said contacts as the liquid is withdrawn.
 4. A system as set forth in claim 2 wherein said compartment inclUdes a floor, said aperture being spaced above said floor, whereby contaminants may settle onto said floor if said pump is inoperative.
 5. A system as set forth in claim 4 wherein said compartment includes baffle means for directing flow of liquid toward said floor for sweeping contaminants therefrom upon operation of said pump.
 6. A system as set forth in claim 5 wherein said inlet is spaced above said contacts.
 7. A system as set forth in claim 5 wherein said compartment includes at least one wall, said baffle means comprising a panel inside said compartment adjacent said wall, said panel having a lower edge spaced above said floor.
 8. A system as set forth in claim 5 wherein said compartment comprises an inner section constituting said baffle means and having an opening in the bottom thereof, and an outer section having walls relatively closely surrounding walls of said inner section, said outer section having a floor constituting the floor of said compartment, said inner section having at least one wall the lower edge of which is spaced above said floor.
 9. A system as set forth in claim 4 wherein said compartment includes a floor, said aperture being located in a side wall of said compartment adjacent said floor, said compartment including baffle means for directing flow of liquid from said body of liquid through said aperture and toward said floor.
 10. A system as set forth in claim 9 wherein said baffle means comprises a relatively small further compartment having a floor and an open top and positioned on the exterior of said side wall in register with said aperture.
 11. A system as set forth in claim 4 wherein said contacts are adapted to open and close by movement of an operating shaft extending from said compartment, said shaft including a liquid passage, said shaft including also at least one further aperture in said compartment communicating with said passage and constituting said liquid inlet, whereby liquid may be withdrawn from said compartment through said passage.
 12. A system for use in electrical apparatus having contacts immersed in a body of insulating liquid and adapted for opening and closing operation causing arcing therebetween which produces contaminants in the liquid adjacent said contacts, said contaminants tending eventually to disperse throughout said body of liquid, said system comprising: a compartment positioned within said body of liquid for relatively closely confining said contacts, the compartment having a volume substantially less than the volume of said body of liquid, the compartment including an aperture for permitting flow of fluid from said body into the compartment but tending to confine in the compartment contaminants produced by arcing of said contacts; a liquid inlet in said compartment; a filter; means, including a pump, for withdrawing liquid from said compartment through said inlet before contaminants have dispersed significantly beyond the confines of said compartment, pumping the withdrawn liquid through said filter, and returning the filtered liquid to said body of liquid; and means for causing operation of said pump for a time period beginning substantially concurrently with operation of said contacts, whereby contaminants produced in the liquid in said compartment by arcing of said contacts are filtered out and thus removed without being permitted to disperse throughout said body of liquid.
 13. A system as set forth in claim 12 wherein said means for causing operation of said pump comprises a time delay relay.
 14. A system as set forth in claim 13 further comprising at least one magnetic contactor adapted to effect operation of said contacts, and also adapted to energize said time delay relay when operation of said contacts is effected. 